With the recent development of information and communication technology, the application to millimeter wave band devices for consumer use is expected. The millimeter wave band is used for, for instance, high-speed transmission of digital signals or automobile radars. For the personal devices, smallness, thinness, and low cost are required. As such, for present digital signal transmission or automobile radars, transmission lines or antennas are formed on resin substrates. Thereby, the requirements for the smallness, thinness, and low cost are intended to be met.
As an example of this device, a high-frequency module is disclosed in Patent Document 1. The high-frequency module includes a high-frequency line 102 formed on a surface of a dielectric substrate 101, a frame-like connection electrode 104 formed on a lower surface of the dielectric substrate 101 just below one end of the high-frequency line 102, an interconnection substrate 100B having a waveguide part 107 in which a conductor layer 106 is formed on an inner surface of a through-hole 105 and an upper end of the conductor layer 106 is electrically connected to the connection electrode 104 throughout a circumference thereof, and a conversion part 103 converting a transmission mode of transmitting the high-frequency line 102 into a waveguide mode of transmitting the waveguide part 107 (see FIG. 18).
The high-frequency module disclosed in Patent Document 1 converts the transmission mode of the signal transmitted to the high-frequency line 102 inside a high-frequency substrate 100A into the waveguide mode, and transmits the signal to the interconnection substrate 100B connected to the high-frequency substrate 100A via the waveguide part 107.
However, the technology disclosed in Patent Document 1 has several problems. Among such problems, one is due to the use of solder, or the like to ensure reliable connection to the waveguide part. The use of solder, or the like is for preventing a phenomenon in which, when a gap is generated to make an incomplete electrical connection at the connection part of a waveguide, the signal leaks out from the waveguide to increase an insertion loss. However, when an amount of the solder on a connection surface is less than a required amount, the electrical connection is made incomplete. Further, when the amount of the solder on a connection surface is more than a required amount, the solder leaks to an undesired part outside the connection part, and thus the waveguide has a shape different from its design at the connection part. In either case, the insertion loss is increased.
Thus, due to the use of solder, or the like, there is another problem in that material or assembly costs are increased.
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2006-041966 (FIG. 1)